Osteogenic Protein-1 of human origin (hOP-1), described in U.S. Pat. Nos. 5,011,691 and 5,266,683, and in Ozkaynak et al. (1990) EMBO J. 9: 2085-2093, recently has been appreciated to be competent to induce genuine tissue morphogenesis in mammals, including the endochondral morphogenesis of bone. It has further been appreciated that mouse OP-1 (see U.S. Pat. No. 5,266,683) and the Drosophila melanogaster gene product 60A, described in Wharton et al. (1991) Proc. Natl. Acad. Sci. USA 88:9214-9218 similarly induce true tissue morphogenesis in mammals. A recent study showed that mice lacking OP-1 display severe defects in kidney and eye development and skeletal abnormalities in the rib cage, skull and hind limbs (Dudley et al. (1995) Genes & Devel. 9:2795-2807 and Luo et al. (1995) Genes & Devel. 9: 2808-2820). Related proteins, including OP-2 (Ozkaynak (1992) J. Biol. Chem. 267:25220-25227 and U.S. Pat. No. 5,266,683); BMP5, BMP6 (Celeste et al. (1991) Proc. Natl. Acad. Sci. USA 87:9843-9847, Vgr-1 (Lyons et al. (1989) Proc. Natl. Acad. Sci. USA 86:4554-4558), and the like are similarly believed to be competent to induce true morphogenesis of mammalian tissue. As a result, significant effort has been devoted to characterizing and developing these and other functionally and structurally related proteins (collectively, morphogens) for use in the regenerative healing of injured or diseased mammalian tissues or organs. Particular effort has been devoted to developing morphogen-based therapeutics for the treatment of injured or diseased mammalian bone tissue, including for example, therapeutic compositions for inducing regenerative healing of bone defects such as fractures, as well as for preserving or restoring healthy metabolic properties in diseased bone tissue, e.g., osteopenic bone tissue. Complete descriptions of efforts to develop and characterize morphogen-based therapeutics for use in mammals, including humans, are set forth in pending U.S. patent application Ser. Nos. 08/404,113, 08/396,930, 08/445,467, 08/152,901, 08/432,883, 08/155,343, 08/260,675, 08/165,541, 08/174,605 and 07/971,091, the teachings of each of which are incorporated herein by reference.
Certain complications, however, presently are encountered during the production, formulation and use in vivo of therapeutic macromolecules, such as morphogen proteins. For example, such proteins are typically produced by fermentation or culture of suitable host cells. Any biological product produced from such host cells for use in humans presently must be shown to be essentially free of host cell contaminants, such as secreted or shed proteins, viral particles or degradation products thereof. Providing such assurance can add significantly to the cost and technical difficulty of commercial production of biological macromolecules. Furthermore, appropriate formulations must be developed for conferring commercially reasonable shelf life on the produced macromolecule, without significant loss of biological efficacy. An additional complicating factor arises when circumstances warrant an extended course of therapeutic treatment with the produced and formulated macromolecule: the treated mammal may develop an immunological response to the macromolecule, and any such response may interfere with effectiveness thereof. In extreme circumstances, treatment must be discontinued.
Accordingly, the need remains for the identification of therapeutically effective analogs of the aforesaid morphogens, particularly for analogs that are inexpensive to produce, are robust upon storage, and have a reduced propensity for eliciting undesirable side effects upon chronic or repeated administration to a mammal.
It is an object of the invention described herein to provide methods and compositions for identifying a morphogen analog, that is, for identifying a substance that mimics a morphogen biological effect in living cells or tissue. It is a further object of the present invention to provide an analog identified according to the present identification method. It is yet a further object to provide a therapeutic composition comprising an identified analog suitable for administration to a mammal in need thereof, such as a mammal afflicted with a metabolic bone disease, e.g., a disease characterized by osteopenia.